Manipal International University Additional Tutorial (3 phase) 1.
A balanced star connected load of (8+j6) ohms per phase is connected to a balanced 3 phase 400V supply. Find the line current, power factor, power and total volt amperes. (Ans:23.1A, 0.8 lag, 12,800W, 16,000VA)
2.
Phase voltage of a star connected alternator are Er=231∟0°V; Ey=231∟-120°V; and Eb=231∟+120°V.what is the phase sequence of the system ?compute the line voltages Ery and Eyb ? ( Ans: Ery=Eyb=400V )
3.
Three equal star connected inductors take 8kW at a power factor 0.8 when connected across a 460V,3 phase, 3 phase 3 wire supply.Find the circuit constants of the load per phase. (ans: IL=12.55A , =Iph. Vph=265 V, VL=460V, iph=21.1A, Rph=16.9ohms, Xph=12.66ohms.)
4.
Given a balanced 3-phase wire system with Y-connected load for which line voltage is 230V and impedance of each phase is (6+j8) ohm. Find the line current and power absorbed by each phase. (Ans: IL=Iph=13.3A,1061W)
5.
Calculate the active and reactive components in each phase of Y-connected 10,000V,3-phase alternator supplying 5000kW at 0.8p.f.If the total current remains the same when the load p.f is raised to 0.9,find the new output. (Ans: 288.8A,216.6A,net power=5625W)
6.
Each phase of a star connected load consists of a non reactive resistance of 100 ohms in parallel with a capacitance 0f 31.8μF.Calculate the line current, the power absorbed, the total kVA and the power factor when connected to a 416V,3-phase,50Hz supply. (Ans: IL=3.39A, pf=0.707, total power=1.728kW,2.433kVA)
7.
A star connected alternator supplies a delta connected load. The impedance of the load branch is (8+j6) ohms/phase.The line voltage is 230V.Determine (a) current in the load branch. (b) power consumed by the load. (c ) power factor of load. (d) reactive power of the load. (Ans: 230v, a=23A,b=12,684W c=0.8 ,d=9513W)
8.
A 220v,3-phase voltage is applied to a balanced delta-connected 3 phase load of phase impedance (15+j20)ohms. (a)
Find the phasor current in each line(Ans: 15.25v)
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Manipal International University (b)
what is the power consumed per phase ?(ans:462W)
(c ) what is the phasor sum of the three line currents ?why does it have this value ?(ans: phasor sum =zero) 10.
A Δ connected balanced 3 phase load is supplied from a 3 phase,400V supply. The line current is 20A and the power taken by the load is 10,000W.Find (i) impedance in each branch (ii)the line current; power factor and power consumed if the same load is connected in star. (Ans: i=34.64 ohms. 0.7217. ii) IL=Iph=20/2 A ,power consumed 3330W)
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